Design Reference

Figure 28: Multiple regions separated by IBGP
In the preceding figure, consider the following
• The AS is divided into three regions that each run different and independent IGPs.
• Regions logically interconnect by using a full-mesh IBGP, which also provides Internet
connectivity.
• Internal nonBGP routers in each region default to the BGP border router, which contains
all routes.
• If the destination belongs to another region, the traffic is directed to that region; otherwise,
the traffic is sent to the Internet connections according to BGP policies.
To configure multiple policies between regions, represent each region as a separate AS.
Implement EBGP between ASs, and implement IBGP within each AS. In such instances, each
AS injects its IGP routes into BGP where they are propagated to all other regions and the
Internet.
The following figure shows the use of EBGP to join several ASs.
Layer 3 network design
70 Network Design Reference for Avaya VSP 4000 February 2014
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